Thyroid Cancer

Thyroid cancer

Definition

Thyroid cancer is a disease in which the cells of the thyroid gland become abnormal, grow uncontrollably and form a mass of cells called a tumor.

Description

The thyroid is a hormone-producing, butterfly-shaped gland located in the neck at the base of the throat. It has two lobes, the left and the right. The thyroid uses iodine, a mineral found in some foods, to make several of its hormones. Thyroid hormones regulate essential body processes such as heart rate, blood pressure, body temperature, metabolism, and affect the nervous system, muscles and other organs. These hormones also play an important role in regulating childhood growth and development.

5-7% of thyroid cancers Found in calcitonin-producing cells Difficult to control as it often spreads to other parts of the body

80% of patients will live for at least 10 years after surgery

Anaplastic

2% of thyroid cancers Fastest growing Rapidly spreads to other parts of the body

3-17% of patients will survive for five years

Types of thyroid cancer

Thyroid cancer is grouped into four types based on how its cells appears under a microscope. The types are papillary, follicular, medullary and anaplastic thyroid cancers. They grow at different rates and can spread to other parts of the body if left untreated.

PAPILLARY.

The papillary type (60%-80% of all thyroid cancers) is a slow-growing cancer that develops in the hormone-producing cells that contain iodine.

FOLLICULAR.

The follicular type (30%-50% of thyroid cancers) also develops in the hormone-producing cells.

MEDULLARY.

The medullary type (5%-7% of all thyroid cancers) develops in the parafollicular cells (also known as the C cells) that produce calcitonin , a hormone that does not contain iodine.

ANAPLASTIC.

The fourth type of thyroid cancer, anaplastic (2% of all thyroid cancers), is the fastest growing, most aggressive thyroid cancer type.

Demographics

Diseases of the thyroid gland affect millions of Americans. The most common diseases of the thyroid are either hyperthyroidism (Grave's disease) or hypothyroidism, an overactive or an underactive gland, respectively. Sometimes lumps or masses may develop in the thyroid. Although most (95%) of these lumps or nodules are non-cancerous (benign), all thyroid lumps should be taken seriously. The American Cancer Society estimates that in 2001, approximately 19, 500 new cases of thyroid cancer will have been diagnosed in the United States.

Women are three times more likely to develop thyroid cancer than men. Although the disease affects teenagers and young adults, most people who develop thyroid cancer are over 50 years of age. Caucasians are affected more often than African-Americans.

Causes and symptoms

The exact cause of thyroid cancer is not known but some risk factors have been identified. Radiation was used in the 1950s and 1960s to treat acne and to reduce swelling in infections of the tonsils, adenoids and lymph nodes. It has been proven that this exposure is a risk factor for thyroid cancer. In some areas of the world, diets are low in iodine. Papillary and follicular cancers occur more frequently in these areas. Iodine deficiency is not a large problem in the United States because iodine is added to table salt and other foods. Approximately 7% of thyroid cancers are caused by the alteration (mutation) of a gene called the RET onco-gene, which can be inherited.

Symptoms are rare, and the lump is not usually painful. The symptoms of thyroid nodules are:

A lump or nodule that can be felt in the neck is the most frequent sign of thyroid cancer.

The lymph nodes may be swollen and the voice may become hoarse because the tumor presses on the nerves leading to the voice box.

Some patients experience a tight or full feeling in the neck and have difficulty breathing or swallowing.

Diagnosis

Physicians use several tests to confirm the suspicion of thyroid cancer, to identify the size and location of the lump and to determine whether the lump is non-cancerous (benign) or cancerous (malignant).

A blood test called the thyroid stimulating hormone (TSH) test checks thyroid function. The blood is drawn by a technician with a needle and the test takes a few
minutes. The results take several days to be interpreted by a pathologist.

A test known as the calcitonin test may be ordered. Calcitonin is a hormone produced by the C cells (parafollicular cells) of the thyroid gland. The hormone is produced in excess when the parafollicular cells of the thyroid become cancerous. Blood calcitonin levels are used to confirm the diagnosis of medullary thyroid cancer if it is suspected.

Computed tomography scan (CT scan) or ultra-sonography (an ultrasound scan) are imaging tests used to produce a picture of the thyroid. A radiologist usually interprets the results of these tests within 24 hours. In ultrasonography, high-frequency sound waves are bounced off the thyroid. The pattern of echoes that is produced by these waves is converted into a computerized image on a television screen. This test can determine whether the lumps found in the thyroid are benign fluid-filled cysts or solid malignant tumors.

A radioactive scan (a thyroid nuclear medicine scan ) may take several hours and can be used to identify any abnormal areas in the thyroid. For this test, the patient is given a very small amount of radioactive iodine which can either be swallowed or injected. Since the thyroid is the only gland in the body that absorbs iodine, the radioactive iodine accumulates there. An x-ray image can then be taken or an instrument called a "scanner" can be used to identify areas in the thyroid that do not absorb iodine normally. These abnormal spots are called "cold spots" and further tests are performed to check whether the cold spots are benign or malignant tumors. If a significant amount of radioactive iodine is concentrated in the nodule, then it is termed "hot" and is usually benign. Again a radiologist interprets the results within a day.

The most accurate diagnostic tool for thyroid cancer is a biopsy . In this process, a sample of thyroid tissue is withdrawn and examined under a microscope by a pathologist. This usually takes a day or so. The tissue samples can be obtained either by drawing out a sample of tissue through a needle (needle biopsy) or by surgical removal of the nodule (surgical biopsy). A needle biopsy takes a few minutes and can be done by any trained physician, usually a radiologist. The surgical biopsy is done by a surgeon under general anesthesia with the help of an anesthesiologist and will take a few hours. If thyroid cancer is diagnosed, further tests may be done to learn about the stage of the disease and help doctors plan appropriate treatment.

Treatment team

The types of healthcare providers often involved in the care of patients are surgeons, internal medicine specialists, pathologists, radiologists, endocrinologists, anesthesiologists, hematologist-oncologists (cancer specialists) and radiation-oncologists.

Clinical staging, treatment and prognosis

Staging

The aggressiveness of each type of thyroid cancer is different. Cancer staging considers the size of the tumor, whether it has grown into surrounding lymph nodes and whether it has spread to distant parts of the body (metastasized). Age and general health status are also taken into account. The American Joint Commission on Cancer (AJCC) staging is summarized below for each thyroid cancer type.

PAPILLARY AND FOLLICULAR.

In patients younger than 45 years:

Stage I refers to patients without evidence of cancer beyond the thyroid.

Stage II refers to patients with spread of cancer outside the thyroid gland.

In patients over 45:

Stage I: Tumors are smaller than one cm (0.3 in).

Stage II: Tumors have not broken through the capsule (covering) of the thyroid.

In the case of Stage IV cancer, the places to which thyroid cancer often metastasizes are the lungs and bone.

MEDULLARY.

Stage I: Tumor is less than 1 cm (0.3 in) or is only detected by a provocative screening test.

Stage II: Tumor is between 1 and 4 cm (between 0.3 and 1.5 in).

Stage III: Nearby lymph nodes reveal cancer.

Stage IV: Evidence of distant metastases.

ANAPLASTIC.

All cases of anaplastic thyroid cancer are considered Stage IV, because this cancer is extremely aggressive.

Treatments

Papillary thyroid cancer can be treated successfully. Follicular thyroid cancer also has a good cure rate but may be difficult to control if the cancer invades blood vessels or grows into nearby structures in the neck.
Medullary thyroid cancers are more difficult to control because they often spread to other parts of the body. Anaplastic thyroid cancer is the fastest growing and tends to respond poorly to all treatments.

Like most cancers, cancer of the thyroid is best treated when it is found early by a primary physician. Treatment depends on the type of cancer and its stage. Four types of treatment are used: surgical removal, radiation therapy , hormone therapy, and chemotherapy .

SURGERY.

Surgical removal is the usual treatment if the cancer has not spread to distant parts of the body. It is the primary treatment for earlier stage papillary, follicular, and medullary thyroid cancers. The surgeon may remove the side or lobe of the thyroid where the cancer is found (lobectomy ) or all of it (total thyroidectomy). If the adjoining lymph nodes are affected, they may also be removed during surgery.

RADIATION.

For papillary and follicular thyroid cancers, radioactive iodine may be used in addition to surgery. In this treatment, the patient would be asked to swallow a drink containing radioactive iodine. Because the thyroid cells take up iodine, the radioactive iodine collects in any thyroid tissue remaining in the body and kills the cancer cells. External beam radiation may also be used if the radioactive iodine is unsuccessful.

For medullary cancers, radioactive iodine is not used. External beam radiation may be used as a palliative therapy. (A palliative therapy is one intended to make the patient more comfortable, not to cure the cancer.)

HORMONE THERAPY.

When the thyroid gland is removed and levels of thyroid hormones decrease, the pituitary gland produces TSH that would normally stimulate the thyroid gland to make thyroid hormone. TSH also stimulates thyroid cells to grow, and it probably also promotes thyroid cancer growth. Hormone therapy uses hormones after surgery to stop this growth and the formation of new cancerous thyroid cells. To prevent cancerous growth, the natural hormones that are produced by the thyroid are taken in the form of a pill. Thus, their levels remain normal and inhibit the pituitary gland from making TSH. If the cancer has spread to other parts of the body and surgery is not possible, hormone treatment is aimed at killing or slowing the growth of cancer cells throughout the body.

CHEMOTHERAPY.

For advanced thyroid cancers for which surgery was not an option or that have not responded well to other treatments, chemotherapy may be tried. For advanced papillary, follicular, and anaplastic thyroid cancers, no chemotherapeutic regimen can be considered standard, and several clinical studies may be ongoing for which patients with these cancers may be eligible. For
anaplastic thyroid cancer, some chemotherapeutic agents (doxorubicin , doxorubicin/ cisplatin combination) have effected partial remission in some patients, but not on a large scale. Patients with anaplastic thyroid cancer may also be eligible for ongoing clinical trials .

Prognosis

More than 90% of patients who are treated for papillary or follicular cancer will live for 15 years or longer after the diagnosis of thyroid cancer. Eighty percent of patients with medullary thyroid cancer will live for at least 10 years after surgery. Three to seventeen percent of patients with anaplastic cancer survive for five years.

Alternative and complementary treatments

Alternative treatments are treatments used instead of conventional treatments. Complementary therapies are intended to supplement traditional therapies and usually
have the objective of relieving symptoms or helping cancer patients cope with the disease or traditional treatments. Common complementary therapies that may be employed by cancer patients are aromatherapy, art therapy, journal therapy, massage, meditation, music therapy, prayer, t'ai chi, and yoga or other forms of exercise, which can reduce anxiety and increase a patient's feeling of well-being. A well-balanced diet can also enhance a patient's sense of well-being, and can help cancer patients better manage their treatments and the side effects of those treatments.

A powerful phytochemical (a chemical found in plants), lycopene, gives tomatoes their red color and appears to act as an antioxidant. Antioxidants such as lycopene help inhibit DNA oxidation (which can lead to certain forms of cancer), repair damaged cells, and scavenge free radicals. (Free radicals are the molecules thought to be responsible for most types of degenerative diseases and aging.) While it is not being suggested that thyroid cancer could be prevented with antioxidants, patients receiving plenty of antioxidants in their diets may feel healthier and more energetic. Lycopene is a normal constituent of human blood and tissues, where it is found in greater concentrations than beta-carotene or any other carotenoid. Tomatoes, including cooked or processed tomatoes, tomato juices, soups, sauces, paste and ketchup, contain more lycopene than any other food. Guava, rose hip, watermelon and grapefruit also contain lycopene.

Other antioxidants are: Vitamin E, Vitamin C, Beta carotene, Lutein, Pycnogenol, Green tea, Grape-seed extract, Alpha lipoic acid, N-acetylcysteine, and Selenium. Pregnant women should consult a physician before taking any medication, and all patients should discuss the complementary therapies and nutritional supplements they are considering with their physician. Some therapies may interfere with patients' prescribed treatments.

Coping with cancer treatment

After thyroid surgery, some patients experience:

difficulty swallowing

voice change

damage to the parathyroid glands

To cope with difficult swallowing, once patients are able to eat after the surgery, many patients start with soft foods, like milkshakes, bananas, applesauce, yogurt, mashed potatoes, and pureed foods. A consultation before the surgery with a dietitian may be helpful, so that the patient can be prepared.

Hoarseness after surgery is usually temporary. Patients may have difficulty hitting high notes when singing, but, the voice change and hoarseness is usually not a major issue for most patients. (Professional singers are advised to discuss their surgery in great detail with their surgeons beforehand.)

If all four parathyroid glands are injured or damaged, it may be necessary for patients to take calcium supplements for a few weeks. Rarely, these supplements may be prescribed for longer periods of time, or even indefinitely.

After radioiodine treatment, some patients experience neck tenderness, nausea and stomach irritation, and dry mouth (xerostomia ). These side effects are rare, but if they occur, patients can try to eat foods that are easy to digest, drink plenty of water to keep the mouth and throat moist, keep lips moist with lip balm, and patients can try sucking on hard candies to alleviate the dry mouth.

The side effects of chemotherapy are bone marrow suppression causing anemia and low platelets. This causes weakness or bleeding. Other problems are nausea and vomiting , hair loss (alopecia ), and inflammation of the oral mucosa. The symptoms are improved with medications.

Depression , if it occurs, is often temporary and can be managed by counseling and family support. Medication is usually not necessary.

Clinical trials

In 2001, seven clinical trials were taking place for patients diagnosed with various types of thyroid cancer. Some of these trials were studying the effectiveness of radioimmunotherapy and peripheral stem cell transplants, combination chemotherapy (using such drugs as paclitaxel , trastuzumab , and interleukin-12), and vaccine therapy. Information about current clinical trials is available through the National Institutes of Health.

Prevention

Because most people with thyroid cancer have no known risk factor, it is not possible to prevent this disease completely. However, the risk for radiation-related thyroid cancer can be reduced by avoiding radiation to the neck when possible, and inherited cases of medullary thyroid cancer can be prevented. If a family member has had this disease, the rest of the family can be tested and treated early. Carriers of the RET mutation may want to consider undergoing prophylactic thyroidectomy at an early age. The National Cancer Institute recommends that every one or two years, a doctor examine anyone who has received radiation to the head and neck during
childhood. The neck and the thyroid should be carefully examined for any lumps or enlargement of the nearby lymph nodes. Ultrasound may also be used to screen for the disease in people at risk for thyroid cancer.

Special concerns

Complications of surgery are very rare with experienced surgeons. Sometimes injury to the nerves in the neck can cause a husky voice or difficulty singing high notes. This can be improved with collagen injection after surgery. Occasionally there is bleeding after the surgery and the incision is reopened to evacuate the clot and stop the bleeding. Patients may have a slightly increased risk of developing another cancer (such as leukemia) in the future after undergoing radioiodine treatment, but this correlation has not been proven. Because thyroid cancers may grow slowly and may recur decades after treatment, follow-up care is important.

See Also Endocrine system tumors; Head and neck cancers; Multiple endocrine neoplasia syndromes

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Thyroid Cancer

Thyroid Cancer

Definition

Thyroid cancer is a disease in which the cells of the thyroid gland become abnormal, grow uncontrollably, and form a mass of cells called a tumor.

Description

Thyroid cancer is grouped into four types based on how its cells appear under a microscope. The types are papillary, follicular, medullary and anaplastic thyroid cancers. They grow at different rates and can spread to other parts of the body if left untreated.

The thyroid is a hormone-producing butterfly-shaped gland located in the neck at the base of the throat. It has two lobes, the left and the right. The thyroid uses iodine, a mineral found in some foods, to make several of its hormones. Thyroid hormones regulate essential body processes such as heart rate, blood pressure, body temperature, metabolism; and affect the nervous system, muscles and other organs. These hormones also play an important role in regulating childhood growth and development.

Diseases of the thyroid gland affect millions of Americans. The most common diseases of the thyroid are either hyperthyroidism (Graves' disease) or hypothyroidism, an overactive or an underactive gland, respectively. Sometimes lumps or masses may develop in the thyroid, and although most (ninety-five percent) of these lumps or nodules are noncancerous (benign), all thyroid lumps should be taken seriously. The American Cancer Society estimates that the approximately 17,200 new cases of thyroid cancer that occur in the United States account for 1% of all cancers.

Women are three times more likely to develop thyroid cancer than men. Although the disease affects teenagers and young adults, most people that develop thyroid cancer are over 50 years of age.

Causes and symptoms

The exact cause of thyroid cancer is not known; but it is more common in whites than in African Americans. Radiation was used in the 1950s and 1960s to treat acne and to reduce swelling in infections of the tonsils, adenoids and lymph nodes. It has been proven that this exposure is a risk factor for thyroid cancer. In some areas of the world, diets are low in iodine. Papillary and follicular cancers occur more frequently in these areas. Iodine deficiency is not a large problem in the United States because iodine is added to table salt and other foods. Approximately 7% of thyroid cancer are caused by the alteration (mutation) of a gene called the RET gene, which can be inherited.

Symptoms are rare so the lump is not usually painful. The symptoms of thyroid nodules are:

a lump or nodule that can be felt in the neck is the most frequent sign of thyroid cancer

the lymph nodes may be swollen and the voice may become hoarse because the tumor presses on the nerves leading to the voice box

some patients experience a tight or full feeling in the neck and have difficulty breathing or swallowing

Diagnosis

Physicians use several tests to confirm the suspicion of thyroid cancer, to identify the size and location of the lump and to determine whether the lump is noncancerous (benign) or cancerous (malignant). Blood tests such as the thyroid stimulating hormone (TSH) test check thyroid function. These are drawn by a technician with a needle and takes a few minutes. It take several days to be interpreted by a pathologist. Calcitonin is produced by the C cells (parafollicular cells) of the thyroid gland when the parafollicular cells of the thyroid become cancerous. Blood calcitonin levels are used to confirm the diagnosis of medullary thyroid cancer if it is suspected.

Computed tomography scan (CT scan) or an ultrasonography (ultrasound scan) are imaging tests used to produce a picture of the thyroid and usually last less than one hour. A radiologist usually interprets the results within 24 hours. In ultrasonography, high-frequency sound waves are bounced off the thyroid. The pattern of echoes that is produced by these waves is converted into a computerized image on a television screen. This test can determine whether the lumps found in the thyroid are benign fluid-filled cysts or solid malignant tumors.

A radioactive scan may take several hours and can be used to identify any abnormal areas in the thyroid by giving the patient a very small amount of radioactive iodine, which can either be swallowed or injected into the thyroid. Since the thyroid is the only gland in the body that absorbs iodine, the radioactive iodine accumulates there. An x-ray image can then be taken or an instrument called a "scanner" can be used to identify areas in the thyroid that do not absorb iodine normally. These abnormal spots are called "cold spots" and further tests are performed to check whether the cold spots are benign or malignant tumors. If a significant amount of radioactive iodine is concentrated in the nodule, then it is termed "hot" and is usually benign. Again a radiologist interprets the results within a day.

The most accurate diagnostic tool for thyroid cancer is a biopsy. In this process a sample of thyroid tissue is withdrawn and examined under a microscope by a pathologist. This usually takes a day or so. The tissue samples can be obtained either by drawing out a sample of tissue through a needle (needle biopsy) or by surgical removal of the nodule (surgical biopsy). A needle biopsy takes a few minutes and can be done by any trained physician, usually a radiologist. The surgical biopsy is done by a surgeon under general anesthesia with the help of an anesthesiologist and will take a few hours. If thyroid cancer is diagnosed, further tests may be done to learn about the stage of the disease and help doctors plan appropriate treatment.

Treatment

The aggressiveness of each type of thyroid cancer is different. Cancer staging considers the size of the tumor, whether it has grown into surrounding lymph nodes and whether it has spread to distant parts of the body (metastasized). Age and general health status are also taken into account. In patients less than 45 years old there are only two stages. I papillary or follicular type thyroid cancer, stage I refers to patients without evidence of cancer that has spread to the body. Stage II refers to patients with spread of cancer outside the thyroid gland. In patients over 45, patients with tumors smaller than one cm are classified as stage I, those with tumors not broken through the capsule (covering) of the thyroid belong to stage II, those with tumors outside the capsule or lymph node involvement are called stage III and those with spread outside the thyroid area are stage IV. In medullary—type thyroid cancer, stage I and IV are the same. Stage II consists of patients with tumors greater than one cm and stage III comprises patients with lymph node involvement.

The papillary type (60-80% of all thyroid cancers) is a slow-growing cancer that develops in the hormone-producing cells (that contain iodine) and can be treated successfully. The follicular type (30-50% of thyroid cancers) also develops in the hormone-producing cells, has a good cure rate but may be difficult to control if the cancer invades blood vessels or grows into nearby structures in the neck. The medullary type (5-7% of all thyroid cancers) develops in the parafollicular cells (also known as the C cells) that produce calcitonin, a hormone that does not contain iodine. Medullary thyroid cancers are more difficult to control because they often spread to other parts of the body. The fourth type of thyroid cancer, anaplastic (2% of all thyroid cancers), is the fastest-growing and is usually fatal because the cancer cells rapidly spread to the different parts of the body.

More than 90% of patients who are treated for papillary or follicular cancer will live for 15 years or longer after the diagnosis of thyroid cancer. Eighty percent of patients with medullary thyroid cancer will live for at least 10 years after surgery. Only 3-17% of patients with anaplastic cancer survive for five years.

Like most cancers, cancer of the thyroid is best treated when it is found early by a primary physician. Treatment depends on the type of cancer and its stage. Four types of treatment are used: surgical removal, radiation therapy, hormone therapy and chemotherapy. Surgical removal is the usual treatment if the cancer has not spread to distant parts of the body.

The surgeon may remove the side or lobe of the thyroid where the cancer is found (lobectomy) or all of it (total thyroidectomy ). If the adjoining lymph nodes are affected, they may also be removed during surgery. When the thyroid gland is removed and levels of thyroid hormones decrease, the pituitary gland starts to produce TSH that stimulates the thyroid cells to grow.

A radiation-oncologist uses radiation therapy with high-energy x-rays to kill cancer cells and shrink tumors. The radiation may come from a machine outside the body (external beam radiation), or the patient may be asked to swallow a drink containing radioactive iodine. Because the thyroid cells take up iodine, the radioactive iodine collects in any thyroid tissue remaining in the body and kills the cancer cells. A hematologist-oncologist uses chemotherapy either as a pill or an injection through a vein in the arm.

Alternative treatment

Hormone therapy uses hormones after surgery to stop this growth and the formation of new cancerous thyroid cells. To prevent cancerous growth, the natural hormones that are produced by the thyroid are taken in the form of pills. Thus, their levels remain normal and inhibit the pituitary gland from making TSH. If the cancer has spread to other parts of the body and surgery is not possible, hormone treatment is aimed at killing or slowing the growth of cancer cells throughout the body.

KEY TERMS

Biopsy— The surgical removal and microscopic examination of living tissue for diagnostic purposes.

Calcitonin— A hormone produced by the parafollicular cells (C cells) of the thyroid. The main function of the hormone is to regulate calcium levels in body serum.

Chemotherapy— Treatment of cancer with synthetic drugs that destroy the tumor either by inhibiting the growth of the cancerous cells or by killing them.

Hormone therapy— Treatment of cancer by inhibiting the production of hormones such as testosterone and estrogen.

Hyperthyroidism— A condition in which the thyroid is overactive due to overstimulation of the thyroid cells.

Hypothyroidism— A condition in which the thyroid gland is underactive.

Total thyroidectomy— A surgical procedure that removes the entire thyroid gland.

A powerful phytochemical, lycopene, gives tomatoes their red color and appears to act as an antioxidant in the body, repairing damaged cells and scavenging free radicals, the molecules responsible for most types of degenerative diseases and aging. Antioxidants such as lycopene help inhibit DNA oxidation, which can lead to certain forms of cancer. Lycopene is a normal constituent of human blood and tissues, where it is found in greater concentrations than beta-carotene or any other carotenoid. Tomatoes, including cooked or processed tomatoes, tomato juices, soups, sauces, paste and ketchup, contain more lycopene than any other food. Guava, rose hip, watermelon and grapefruit also contain lycopene.

Prevention

Because most people with thyroid cancer have no known risk factor, it is not possible to completely prevent this disease. However, inherited cases of medullary thyroid cancer can be prevented and radiation to the neck is avoided. If a family member has had this disease, the rest of the family can be tested and treated early. The National Cancer Institute recommends that a doctor examine anyone who has received radiation to the head and neck during childhood at intervals of one or two years. The neck and the thyroid should be carefully examined for any lumps or enlargement of the nearby lymph nodes. Ultrasound may also be used to screen for the disease in people at risk for thyroid cancer.

Citation styles

Encyclopedia.com gives you the ability to cite reference entries and articles according to common styles from the Modern Language Association (MLA), The Chicago Manual of Style, and the American Psychological Association (APA).

Within the “Cite this article” tool, pick a style to see how all available information looks when formatted according to that style. Then, copy and paste the text into your bibliography or works cited list.

Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, Encyclopedia.com cannot guarantee each citation it generates. Therefore, it’s best to use Encyclopedia.com citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:

Modern Language Association

The Chicago Manual of Style

American Psychological Association

Notes:

Most online reference entries and articles do not have page numbers. Therefore, that information is unavailable for most Encyclopedia.com content. However, the date of retrieval is often important. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates.

In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.